It is very important at the present time that the contamination of the environment by any method, whether it be a combustion process or a chemical method, be restricted to a minimum.
For many years, it was customary to purify the gases, which are formed during these processes, in a scrubbing tower, in which the rising gases were scrubbed by being sprayed from above by means of water or a suitable solution. By these means, the pollutants in the gas were dissolved out or separated and concentrated in the scrubbing solution.
To support the scrubbing process, the towers were previously provided with a static packing, which has a large surface area relative to the gas and the water and contributes to washing out the unwanted particles and chemicals from the gas.
To be efficient, the scrubbing towers with stationary packing frequently must be very tall and contain a large amount of packing, so that the gases emerging from it has been purified to such a degree, that the pollutant content is safe for the environment.
To solve this problem, it was proposed that the packing be replaced by spherical column packing material, which is maintained in a fluidized state by the velocity of the gas that is to be purified.
The advantages of using these spheres, which consist of a chemical inert material such as polypropylene, lies therein that the spheres are rotating and moving constantly. For this reason, the particles, which are scrubbed out of the gas, do not adhere to the spheres and thus do not block the scrubbing process or increase the pressure drop.
However, the fluidized spheres have the disadvantage that the fiuidizing gas tends to move the spheres from the center of the tower to the sides. As a result, a hole is left in the center of the tower and the gas can flow through this hole without being subjected to a scrubbing process other than the spraying with water or a different scrubbing liquid. If the gas flows through the spherical packing, turbulence develops, by means of which the scrubbing process is aided.
To solve this problem, it was proposed in the German patent 36 13 151 that ellipsoids be used in a fluidized bed scrubber instead of spheres.
The ellipsoids have a regular shape and a maximum and minimum diameter, the wall being thickened in the region of the larger diameter of the sphere. The ellipsoids are fluidized by the gas stream already at the low velocity of 1 m/sec. The individual ellipsoids carry out directed transverse motions within the individual bed and, at the same time, rotate about the short semiaxis. The use of hollow ellipsoids in gas scrubbers is particularly advantageous, because the film of liquid on the surface of the ellipsoid is frequently torm off by the accelerated rotary motion and the exchange of material is activated by the new formation of the film.
Rotation about its own axis produces a high circumferential velocity in the plane of the long semiaxis. This leads to a directed flow of the scrubbing liquid on the contact surface with intensive distribution from the edge to adjacent contact elements. On the whole, a new, chargeable phase boundary surface for material exchange is thus permanently offered and the absorption performance and the particle precipitation are thus improved.